Causes of Knee Replacement Pain

The most important step in finding a solution to persistent discomfort is to first determine the cause of the pain. Without this knowledge, it is very difficult to find an appropriate treatment. The most common causes of pain after knee replacement include:

Loosening of the Implant

This is most often the cause of pain years or decades after a knee replacement. However, it is seldom the cause of persistent pain right after surgery. In order for a total knee replacement to function properly, an implant must remain firmly attached to the bone. During the initial surgery, it was either cemented into position or bone was expected to grow into the surface of the implant. In either case, the implant was firmly fixed. Over time, however, an implant may loosen from the underlying bone, causing the knee to become painful.

The cause of implant loosening is not always clear, but high-impact activities, excessive body weight, and wear-and-tear of the plastic spacer between the two metal components of the implant are all factors that may contribute. Also, patients who are younger when they undergo the initial knee replacement may "outlive" the life expectancy of their artificial knee. For these patients, there is a higher long-term risk that revision surgery will be needed due to loosening or wear-and-tear.

In some cases, tiny particles that wear off the plastic spacer accumulate around the joint and are attacked by the body's immune system. This immune response also attacks the healthy bone around the implant, leading to a condition called osteolysis. In osteolysis, the bone around the implant deteriorates, making the implant loose or unstable.

Infection

Infection is a serious and worrisome concern. Any increase in pain after knee replacement should raise concerns for infection. Most often, the signs of infection are obvious, but subtle infections may be the cause of persistent discomfort. Infection is a potential complication in any surgical procedure, including total knee replacement. Infection may occur while you are in the hospital or after you go home. It may even occur years later.

If an artificial joint becomes infected, it may become stiff and painful. The implant may begin to lose its attachment to the bone. Even if the implant remains properly fixed to the bone, issues such as pain, swelling, and drainage from the infection may make revision surgery necessary.

Revision surgery for infection can be done in one of two ways, depending on the type of bacteria, how long the infection has been present, the degree of infection, and patient preference.